Frequency changer system



March 29, 1938. R, M' KALB 2,112,533

FREQUENCY CHANGER SYSTEM Filed Sept. 25, 1936 CORE 20-22 45A: n/49 cons /NPur -J lll l/V Bry Arron/Vey Patented Mar. 29, 1938 UNITED STATES PATENT .OFFICE 2,112,533 FREQUEGY CHANGER. SYSTEM Robert M. Kalb, East Orange, N. J., assigner to v Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Appiiation september 23, 193s, serial No. 102,114 11 claims. (ci. 172-281) This invention relates to frequency changer systems Where static frequency-transformers are employed for producing frequencies not present in the applied frequency.

An attribute of all non-linear ferromagnetic coils is their ability to produce frequencies other than those impressed. When an iron Core coil under proper circuit conditions is subjected to a single frequency current it is known that harmonics of the impressed frequency will be generated. An object of the present invention is to provide a magnetic frequency converter whose output frequency is a rational fractional multiple of the input frequency. A more particular object is to provide such a. converter in .the

secondary of which will be found no harmonics of the input frequency but only the odd harmonics of half of the input frequency whereby the frequencies generated for an input frequency In a preferred embodiment the frequency converter of this invention utilizes two magnetic core transformers having the two primary windings connected in series and the two secondarywindings connected in series, the windings being poled as by a reverse connection of the twoprimaries to make the input and output branches conjugate. If it is desired to obtain one of the odd harmonics of half of the input frequency an asymmetrical flux wave of the periodicity of the input frequency is produced in each core, as by applying an asymmetrical wave of the input frequency across the twoprimary windings, and the desired fractional multiple frequency is selected by a. tuned circuit across the two secondary windings. The applied asymmetrical Wave may be obtained by overloading the grid circuit of a vacuum tube amplifier with a sinusoidal wave of the inpt frequency or by using the output of a half wave rectifier driven by a wave of the input frequency to be converted. Still other means for obtaining the desired asymmetry of the input wave may be utilized if desired. .y

Referring to the drawing,

Fig. 1 represents a magnetic frequency converter for obtaining a fractional multiple of the input frequency where an overloaded amplifier is employed for producing an asymmetrical wave which is applied to a magnetic frequency converter to produce an asymmetrical fluir` Wave of the periodicity of the input frequency in its cores;

Fig. 2 is a modification. of Fig. 1;

Fig. 3 is a magnetic frequency converter in which the desired asymmetrical wave of the input frequency is obtained by rectification of the input frequency;

Fig. 4 is a magnetic frequency converter in which the cores of the converter are polarized by a direct current flow through supplementary windings thereon;

Fig. 5 discloses a magnetic frequency converter lo provided with a direct current bias to give the desired asymmetrical wave of the input frequency;

Fig. .6 discloses a converter employing permanent magnets as cores; l5

Fig; 7 is an alternative form of the invention designed to make the selected output frequency substantially independent of small variations in the amplitude of the input frequency or the values of the circuit parameters;

Fig. 8 represents an alternative core construction that may be employed in Figs. 1 to '7; and

Fig. 9 is a curve illustrating the character of the frequency output of the converter of this invention.

In its preferred form this invention involves' the use of transformer cores of a magnetic material such as permalloy which has a very high permeability at low magnetizing forces `and which soon becomes saturated when these forces are increased. thereby reducing the permeability to a low value.

Referring to Fig. 1 an alternating current of a certain frequency f from source I0 is impressed through an input transformer II upon a vacuum tube amplifier I2 in suilicientDamplitude vto overload the grid circuit of the amplifier and drive the grid positive so that the output circuit'of the amplifier includes current not only of the fundamental frequency f but harmonics 40 thereof. The output from amplifier I2 is impressed through output transformer I3 upon the primary windings I4 and I5 of a pair of similar transformers I6 and i7 Whose cores I8 and I9 may as previously stated be of permalloy or` other high permeability material. Across the secondary windings 20, 2l is connected a. series tuned circuit comprisingY an inductance 22 and a capacity 23 for tuning the secondary mesh of the transformers I6, II to the desired odd harmonic of half the fundamental frequency f of source I0.

Since the primary windings I4 and Ii are connected in series opposition the input and output branches of transformers I6 and I'I are conjugate. This arrangement tends to purify the wave form in the output by pre/'venting the setting up of a secondary current of the input frequency through transformer action. This conjugate relationship also prevents the impedance of the primary .branch of the frequency converter from affecting the impedance voi the secondary branch. Another advantage of. the 'conjugate meshes is the discrimination by balancev against extraneous currents in the inputy When the asymmetrical wave of frequency is impressed on coilsl I0 and I1 due to the over'- loaded amplier I2 it hasbeen found that if the series tuned circuit 22, 2l is adjusted to tune,

-ithe secondary brahchof/the coils I6 and I1 to any one of the odd harmonics of half the input u frequency there will be a current of relatively high amplitude of the fractional harmonic selected but 'if the secondary mesh is tuned to a substantially di'erent frequency there will be substantially no current flow through the tuned circuit 22, n. v

Fbr example, if' the input frequency produced by source I0 is 4,000 cycles per second then by proper tuning 'of the secondary mesh 20 to 2l for the desired odd integral multiple of half the input frequency, one may readily obtain with relatively high amplitude current of one of the frequencies 5f 1f 2,000 cycles 6,000 cycles `10,000 cycles (-2-): 14,000 cycles 1f. 4f. etc.

The current of the desired frequency may be supplied to a load circuit in any suitable manner although direct application of large load would be objectionable a's it would 'broaden the frequency response and either would tend to introduce extraneous frequencies `or wouldvs'uppress all oscillations.. It is preferable to interpose an amplifier between theload and the frequency converter having the amplier work from part of thevvoltage across one of thetuningelements or by having the amplifier connected to the secondary mesh of the frequency converter by a high ratio stepuptransformer- In Fig. 1 the primary of avacuum tube input transformer 2l is con-4 nected across'cgndenser 23 so that the amplier 25 prevents thev load from reacting on the secondary mesh of the converter. Taking the load across condenser 21 serves to discriminate against higher extraneous `frequencies in, 'the output mesh;l while taking the load across inductance 22 would discriminate against lower extraneous fre` quencie's.

In a preferred embodiment each of the coils I6 and I1 may have a l to 1 winding ratio with their cores of laminated tape about 1 mil..thick made, for example, of 3.8 per cent chromium permalloy in accordance with the Elmen U. S. Patent No. 1,768,237. The unity ratio, however, is not essential and other kinds of magnetic materials of high permeability may be employed.

An important feature* ot the frequency converter of Fig. 1 is the ability of the output to maintain a fixed frequency relation with the input over a definite range of variation of the input amplitude or the circuit parameters.

Fig. 9 illustrates the relative amplitudes' of the frequencies [availablein the .secondary mesh of the frequency converter of Fig. 1. Inl Fig. 9 the input frequency f appear but that the harmonics current I in the secondary mesh of the converter I6, I1 is plotted against various values of of the input frequency are' absent. The greatest amplitude shown is for tuning to the frequency followed by smaller amplitude peaks for tuning sirable to place the condenser Il in series with the primary windings of the frequency converter as shown in Fig. 2. The inductance 22 of Fig. l is not always necessary and has been omitted in Fig. `2. In Fig. 2 the condenser 1i serves to tune the invariable component of the inductance of the secondary windings 20, 2i to the desired frac tional multiple of the fundamental frequency.

' As previously stated, other means may be employed to produce the desired asymmetrical wave of the fundamental frequency. In Fig. 3 a half wave rectier I3 is inserted in series with source Il so that the rectifier output is supplied to the frequency converter I8, I1. available in the secondary mesh of the converter of Flg.'2 are the same as for Fig. l and as shown in Fig. 9 comprise by proper tuning quency will be present. In Fig. 3 a resistance capacity coupling of a well-known type is employed to impress the voltage across condenser 23 upon an amplifier 34 which serves to impress the selected fractional harmonic uponthe load circuit.

Another way toobtain in thecores ofrthe frequency converter the desired biasing magnetization is by polarizingthe cores I8 and I9 as in Fig'. 4 by placing additional windings, and on the cores I8 and I9 and connecting these additional windings in series with a direct current source 31 and a choke'coil 29. The-frequency output available to the secondary msh of the converter of Fig. 4 is the same as for Fig. I and is shown in Fig. 9. The amplifier 20 is a distortionless amplifier andnot an overloaded amplifier as in the case of Fig. 1 Chokecoil 22 in the direct currentv circuit prevents it from shunting thealternating current.

The desired biasing magnetization may also be obtained by adirect current component supplied The frequencies.,

" ond transformer is with the input wave of the fundamental frequency. This is shown in Fig. where the pri mary windings I4, l5 are traversed by direct current from source 40 connected across the windings in series with adjustable resistance 4|. If desired, battery 40 may be the space current source or B-battery of amplifier 38. An isolating condenser 42 may be employed to direct the direct current through these primary windings, while a choke coil prevents the alternating current from being shunted through battery 40 and resistance 4|. `The frequency output available from the converter to Fig. 5 is the same as that of Fig. 1 as shown in Fig. 9.

Still another way of securing the biasing magnetization for the frequency converter is to employ permanently magnetized cores. In Fig. 6 the two cores 43, 44 are of a permanently magnetized material which saturates at relatively low magnetizing forces. Otherwise, the arrangement of Fig. 6 is similar to that of Fig. 1 with the primary windings 45, 4B reversely poled to make the input and output branches conjugate, the secondary windings 41, 48 being connected in series With a tuned circuit comprising an inductance 49and a capacity 50. As in Fig. 1 the values of inductance 49 and capacity 50 determine which odd harmonic of half the fundamental frequency is supplied to the load circuit. Some understanding of the operation of the circuits of the invention in changing the frequency may be gained from analysis of the output mesh. The voltage induced in a secondary` winding of N2 turns on one transformer core carrying a flux fi is Noo-I'Nii-i-Nziz n where No and N1 represent turns traversed by the biasing and input currents, respectively. Thus `the secondary voltage in the one core may be Where d" (k) denotes the derivative of the ux with respect to the magnetomotive force.

The two transformers of a pair are similar, so that the magnetomotive force producing flux in the core of the other transformer is proportional to The reversed signs are occasioned by the opposite poling of the windings, the only essential difference from the first transformer. In these devices as they operate, the magnetization of the cores is dominated by the input, with the result that the secondary current exerts minor influence on the magnetomotive force. Also, the slope of the magnetization curve depends on only the magnitude of the magnetomotive force and not its direction. The secondary voltage in the sectherefore, to a close approximation yFloquets theory.

'Ihe electromotive force in the two secondary windings connected in series is the sum of e1 and e2, and in this sum the normally transformed voltages induced by the primary current cancel, leaving only an electromotive force proportional to the rate of change of the secondary current and dependent upon the non-linear/characteristics of the core material. In particular, the conjugate connection of the two transformers phases out of the secondary side all harmonic voltages generated by the core in the ordinary manner, as well as the fundamental and harmonic currents suppliedito the primary windings by the driving source. 'Ihe secondary current flows through an inductance L, a resistance R, and a capacity C, in series with the secondary windings of the two transformers. The charge, q, on the condenser is connected with iz by the relation varound the mesh and equating their sum to zero in accordance with Kirchoifs law.

'I'he coeilicient of the second derivative in Equation (4) is periodic intime, a circumstance which accounts for the transfer of energy into the` secondary mesh and endows the current in that mesh with its peculiar properties. vThe nature of the solutions of any linear differential equation with periodic coeflicients has been known to mathematicians for some time through (G. Floquet-Sur les quations differentielles linaires coefficients priodiques. Ann. de. lEcole norm. sup. (2) vol. 12, (1883), pp. 47-88). This yields the result that periodic solutions of such equations period of the coefficients. (E. L. Ince-Ordinary Differential Equations, London 1927, pp. 381 et seq.) Equation (4) thus specifies a charge with a fundamental frequency one half the fundamental frequency of i (k).

The period of @'(k) is that of lc and hence the same as the period of the primary magnetizing current when it includes direct current or even order harmonic components which cause the magnetization curve of the core material to be traversed asymmetrically. If the curve were traversed symmetrically a frequency doubling would occur in the cores; because I (k) is an even function of the magnetomotive force it would vary at twice the frequency of this force. The fundamental frequency of the charge, being half that of @'(k), would then be the same as that of the primary current. It should also be noted that, unless the instantaneous flux components produced in both cores by the alternating current have the same relation to those produced by the direct current, phase displacement between the electromotive forces. in the two secondary windings will result. 'I'his leads to a double-frequency component in @'(k) which produces an electromotive force of fundamental frequency in the secondary windings and a simultaneous reduction of the half-frequency electromotive force. Phase opposition produces complete frequency doubling and only the fundamental frequency and its harmonics then exist in the secondary current.

The above. analysis proves thatthe Waves .ap--

may have twice the frequency stability as pearing in the formers in the secondary mesh of the two transcircuits of the invention as illustrated in the several figures of the drawing and described above, include waves of half the fundamental frequency applied to the primary mesh as well asY harmonics of half the fundamental frequency.

On'e desirable characteristic of the circuits above described is that they lock in at the exact desired frequency ratio and so have the same the input frequency. The converter circuits of the invention constructed as shown in Figs. l tol 'l make operation at unwanted frequencies impossible, thus preventing any chance frequency variation in driving source being transmitted through the converter. The circuitsof this invention also have the advantage that the selected odd harmonic of half the fundamental frequency will be obtained even though small variations occur in the value of the circuit elements, the input amplitude, or the whole. This stability may be termed coherencethe ability of the output to maintain frequency relation with the input over a definite range of variation of the input amplitude or the circuit parameters. However, if the input of the fundamental frequency is subject to substantial variations/Kin amplitude it may be desirable to feed the frequency converters i6, I1 from a constant current amplifier which in the case of Fig. l may be the overloaded ampliflerernployed to produce the asymmetrical wave input.

The increased frequency stability of the circuits of Figs. 1 to 'I is due to the fact that the secondary circuit of the saturable core transformers in each case comprises only one resonant mesh which is tuned to half the frequency applied to the primary circuit of the transformers, or to harmonics of that half frequency. The use of several resonant meshes tuned to different frequencies would provide several degrees of freedom tending to cause oscillations in unwanted modes, i. e., a lack of coherence, which would make the circuit hard to control.

Fig. 7 shows an alternative arrangement for obtaining an odd harmonic of half 'the fundamental frequency without the need of applying an asymmetrical wave to the input of theconverter. The output from the two frequency converter coils i0, I1 comprises a network of two sections( the first section comprising a series inductance 5| and a shunt capacity 62, while the this identical tuning second section comprises an anti-resonant circuit comprising an inductance 53 and a capacity 5l. These two sections may be coupled capacitatively if desired, by condenser 55. The tuned circuit n, si should be made ann-resonant at the desired frequency output so that ifthe input to the frequency converters I6 and I1 from source I0 is 4,000 cycles and 10,000 cycles is desired, thei the circuit 53, 54 should be tuned to 10,000 cycles. 'I'he series tuned circuit Il., 52 of the rst section is employed to increase the stability of the circuit to insure that with a given inp'ut frequency the desired odd harmonic of half the input frel quency will be obtained, under varying conditions of load and circuit parameters. Although inductance' 5| and capacity 52 may also be tuned to the frequency to be selected to obtain this coherence,

of the two sections is not es- 'I does not have -the asymsential. Since Fig.

vmetrical flux wave input of the earlier figures,

the arrangement of Fig. 'I is also capable of generating harmonics of the fundamental frequency by proper tuning of the secondary mesh.

, frequency comprising ananas Fig. 'I a series tuned vcircuit 60, 0I and an antiresonant circuit 02, 0l may be connected in series and in shunt respectively, to the primary windings of the frequency converter, each tuned to the fundamental frequency of source i0. These tuned circuits QI, Il and, Il are not essential, however, to the operation of the converter and may be omitted if desired. y

It should be noted that in general it is not necessary to employ two separate cores for the frequency converter as the primary and secondary windings may be placed on a two-mesh core 65 as shown in lFig. 8 where the common secondary winding 80 for the two primary windings 61, 68 is placed on the center leg .with the two primary windings 6u the two ,outer legs of the core. The two primary windings are connected in series opposition so that the input and output circuits of the coils I6 and I1 o any of the earlier figures. It

may also be noted that, if desired, winding Siif may be-included in the input mesh and windings 61, 68 in the output mesh of the frequency converter instead of the reverse connection indicated on the drawing. l

In the frequency converters of Figs. l to 6 it is to be understood that the amount the flux wave supplied to the frequency converter cores is made asymmetrical depends upon circuit conditions and should be adjusted to`producethe optimum amplitude of the frequency to which the secondary mesh ofthe converter is tuned.

It is to be understood that other embodiments of the invention are contemplated commensurate with the scope of the appended claims.

What is claimed is:

1. A circuit for obtaining rational fractional multiples or submultiples of a given fundamental two inductive windings, an input circuit comprising said two windings connected in, series, magnetic core means for said windings, a secondarywiuding on at least a portion of said core means, an output circuit including said secondary winding, said input and output circuits` being conjugate, a source of an 2. A frequency converter in accordance withu claim 1 in which the means for producing said asymmetrical flux wave comprises a 'vacuum tube amplier coupling'said source and -said two serially connected windings, and means for making the amplitude of the wave'supplied from said source to said amplifier such as to overload it whereby an asymmetrical wave is supplied to said two windings.

3. A frequency converter in accordance with claim 1 in which the means for producing said asymmetrical flux wave comprises a rectifier connected between said source and said two serially connected windings.

4. A frequency converter in accordance with claim 1 in which the means for producing said asymmetrical fiux wave comprises means for superposing on the alternating current wave supplied from said source to said two windings a direct current component such manner as to'make the magnitudes of the instantaneous electromotive forces induced by the alternating component of the flux wave in of said secondary winding substantially equal.

5. A circuit for obtaining rational fractional multiples of a given fundamental frequency comprising a source of an asymmetrical wave of said given frequency, two magnetic core transformers each having a primary winding and a secondary winding, the two ly wound and connected in series across said source,v and an output circuit connected across the two secondary windings in series, said output circuit being tuned to the desired multiple frequency.

6. The circuit of claim 5, in which said source of an asymmetrical wave of said comprises a vacuum tube amplifier having an ply a sinusoidal wave of said given frequency to said input circuit in such manner as to overload said amplifier, said output circuit being connected cuit comprising said windings connected in series,

magnetic core means for said windings, a sec- I `ondary winding on atleast a part of/said core means, an output circuit including said secondary winding, said input and output circuits being conjugate, a source of a given frequency in said input circuit, and means for producing in said core means an asymmetrical ux wave of a perioutput circuit being tuned to an odd harmonic of half the frequency y,of said source.

8. A frequency converter for obtaining an odd harmonic of half a given fundamental frequency having a primary winding and a secondary winding. an input circuit comprising said primary of magnetization in` primary windings being reverseodicity equal to the frequency of said source, said comprising two magnetic core transformers each y windings connected in series, an output circuit comprising said secondary windings, said windings being so related that said input circuit and said output circuit are conjugate, and means for supplying to said input circuit an asymmetrical wave of said given frequency, said output circuit being tuned to the desired odd harmonic of half the frequency of said given frequency.

9. A frequency converter for obtaining an odd harmonic of half a given fundamental frequency comprising two magnetic core transformers each having a primary winding and a secondary Winding, an input circuit comprising said two primary windings connected in series, an output circuit `comprising said secondary windings, said windings being so related that said input circuit and said output circuit are conjugate, a source of a given frequency, -)means for producing in said cores an asymmetrical flux wave of a periodicity equal to the frequency of said source and such that the electromotive forces in all parts of said secondary winding are substantially the same at any instant, a resonant circuit in said output circuit tuned to the desired odd harmonic of half the frequency of said source, a load circuit to be supplied with a frequency equal to the frequency to which said resonant circuit is tuned, and a vacuum tube amplifier interposed between said resonant circuit and said load circuit.

10. A frequency changing device comprising input and output branches, an asymmetrical distorting device coupling said input and output branches in conjugate relation, means for impressing an alternating current wave of a given frequency on said input branch, and a single resonant mesh in said output branch tuned to frequencies other than harmonics of said given frequency.

11. A frequency changer comprising one or more pairs'of oppositely poled transformers having primary and secondary windings and a saturable magnetic core, means to apply a pulsating existing current 'to the primary winding of each pair of transformers, and a single output mesh comprising reactive and resistance circuit elements connected in series with the secondary windings ofeach pair, said circuit elements being so proportioned that the current passing through them will have a periodicity different from that of the exciting current applied to the primary windings of the pair.

' ROBERT M. KALB. 

